Data transmission method and data transmission apparatus

ABSTRACT

This application provides a transmission method and a data transmission apparatus. The method includes: sending, by a source access network device, data packets of a QoS flow and a first end marker packet to a first core network user plane device over a first data tunnel, wherein the first end marker packet indicates an end of sending data packets of the QoS flow to the first core network user plane device, and the first data tunnel is corresponding to a first PDU session; sending, by the first core network user plane device, the data packets received from the source access network device and a second end marker packet to a second core network user plane device over a second data tunnel; and sending, by the second core network user plane device, the data packets received from the first core network user plane device to a target access network device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2018/099967, filed on Aug. 10, 2018, which claims priority toChinese Patent Application No. 201710687846.0, filed with the ChinesePatent Office on Aug. 11, 2017. The disclosure of the aforementioned areincorporated herein by reference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and morespecifically, to a data transmission method and a data transmissionapparatus.

BACKGROUND

In a Long Term Evolution (LTE) communications system, when a terminalmoves on an access network side, a network element of an access networkthat sends and receives data changes, and the network element of theaccess network instructs a network element of a core network to change auser plane data tunnel, thereby ensuring service continuity. However,for a changed user plane data tunnel of the core network, an end markeris sent over the old data tunnel, to notify the end of sending adownlink data packet, where the user plane data tunnel is establishedbased on an evolved packet system (EPS) bearer.

However, in a next-generation communications system, a quality ofservice (QoS) architecture based on a QoS flow is introduced. A datapacket tunnel is established between a network element of a core networkand a network element of an access network based on a packet data unit(PDU) session, and one PDU session may include one or more QoS flows.Therefore, when a terminal is moving, a data tunnel of one or more QoSflows may need to be changed, or a data tunnel of the PDU session mayneed to be changed. How the network element of the core network sets anend marker is a problem that needs to be resolved.

SUMMARY

This application provides a transmission method and a data transmissionapparatus, so as to avoid out-of-order of data packets.

According to a first aspect, a transmission method is provided,including: sending, by a source access network device, a firstproportion of data packets in a first Packet Data Convergence Protocol(PDCP) entity in the source access network device to a target accessnetwork device by using a data tunnel between the source access networkdevice and a second PDCP entity of the target access network device,where the first proportion of data packets are data packets of a firstquality of service (QoS) flow in a first protocol data unit (PDU)session, the first PDU session includes at least one QoS flow, the atleast one QoS flow is in one-to-one correspondence with at least onePDCP entity, the at least one QoS flow includes the first QoS flow, theat least one PDCP entity includes the first PDCP entity, the first PDCPentity corresponds to the first QoS flow, and the first QoS flow is anyone of the at least one QoS flow; and sending, by the source accessnetwork device, first indication information to the target accessnetwork device, where the first indication information is used toindicate that all the first proportion of data packets in the first PDCPentity have been sent.

Optionally, the first indication information includes a largest PDCPsequence number in PDCP sequence numbers carried by all data packets inthe first proportion of data packets; or

the first indication information includes a next to-be-allocated PDCPsequence number; or the first indication information is an end markerpacket generated by the first PDCP entity.

Optionally, before the sending, by the source access network device, afirst proportion of data packets in the first PDCP entity to the targetaccess network device, the method further includes: determining, by thesource access network device, that a first Service Data AdaptationProtocol (SDAP) entity in the source access network device stops sendingdata packets of the first QoS flow to the first PDCP entity, where thedata packets of the first QoS flow that are sent by the first SDAPentity to the first PDCP entity are the first proportion of datapackets, and the first SDAP entity corresponds to the first PDU session.

Optionally, the second indication information is sent by the first SDAPentity based on an end marker packet received from a core network userplane device.

According to a second aspect, a transmission method is provided,including: receiving, by a target access network device by using a datatunnel between a second PDCP entity of the target access network deviceand a first PDCP entity of a source access network device, a firstproportion of data packets sent by the first PDCP entity, where thefirst proportion of data packets are data packets of a first quality ofservice QoS flow in a first protocol data unit PDU session, the firstPDU session includes at least one QoS flow, the at least one QoS flow isin one-to-one correspondence with at least one PDCP entity, the at leastone QoS flow includes the first QoS flow, the at least one PDCP entityincludes the first PDCP entity, the first PDCP entity corresponds to thefirst QoS flow, the second PDCP entity corresponds to the first QoSflow, and the first QoS flow is any one of the at least one QoS flow;and receiving, by the target access network device, first indicationinformation sent by the source access network device, where the firstindication information is used to indicate that the first PDCP entityhas sent all the first proportion of data packets.

Optionally, the method further includes: after determining, based on thefirst indication information, that all data packets in the firstproportion of data packets have been sent to a terminal, sending, by thetarget access network device, a data packet received from a second SDAPentity of the target access network device to the terminal.

Optionally, the first indication information includes a largest PDCPsequence number in PDCP sequence numbers carried by all the data packetsin the first proportion of data packets; or the first indicationinformation includes a next to-be-allocated PDCP sequence number; or thefirst indication information is an end marker packet generated by thefirst PDCP entity.

According to a third aspect, a transmission method is provided,including: if it is determined that a terminal no longer sends a datapacket of at least one quality of service QoS flow in a first PDUsession to a source access network device, generating, by the sourceaccess network device, trigger information; and sending, by the sourceaccess network device, the trigger information to a target accessnetwork device, where the trigger information is used to instruct thetarget access network device to send, to a core network user planedevice, a data packet that is of the at least one QoS flow and that issent by the terminal to the target access network device, and thetrigger information includes an identity of the at least one QoS flowand an identity of the first PDU session; or the trigger informationincludes an identity of the at least one QoS flow and an identity of afirst data radio bearer (DRB), and the first DRB corresponds to the atleast one QoS flow.

According to a fourth aspect, a transmission method is provided,including: receiving, by a target access network device, triggerinformation sent by a source access network device, where the triggerinformation is used to instruct the target access network device tosend, to a core network user plane device, a data packet that is of atleast one quality of service QoS flow in a first PDU session and that issent by the terminal to the target access network device, and thetrigger information includes an identity of the at least one QoS flowand an identity of the first PDU session; or the trigger informationincludes an identity of the at least one QoS flow and an identity of afirst data radio bearer DRB, and the first DRB corresponds to the atleast one QoS flow; and sending, by the target access network device tothe core network user plane device based on the trigger information, thedata packet that is of the at least one QoS flow and that is sent by theterminal to the target access network device.

Optionally, the trigger information is an end marker packet, or thetrigger information is a message between access network devices.

According to a fifth aspect, a transmission method is provided,including: if a source access network device determines that a terminalreceives a data packet that is of at least one quality of service QoSflow in a first PDU session and that is sent by the source accessnetwork device, generating, by the source access network device, triggerinformation; and sending, by the source access network device, thetrigger information to a target access network device, where the triggerinformation is used to instruct the target access network device tostart to send, to the terminal, a data packet that is of the at leastone QoS flow and that is received by the target access network devicefrom a core network user plane device, and the trigger informationincludes an identity of the at least one QoS flow and an identity of thefirst PDU session; or the trigger information includes an identity ofthe at least one QoS flow and an identity of a first data radio bearerDRB, and the first DRB corresponds to the at least one QoS flow.

According to a sixth aspect, a transmission method is provided,including: receiving, by a target access network device, triggerinformation sent by a source access network device, where the triggerinformation is used to instruct the target access network device tostart to send, to a terminal, a data packet that is of at least onequality of service QoS flow in a first PDU session and that is receivedby the target access network device from a core network user planedevice, and the trigger information includes an identity of the at leastone QoS flow and an identity of the first PDU session; or the triggerinformation includes an identity of the at least one QoS flow and anidentity of a first data radio bearer DRB, and the first DRB correspondsto the at least one QoS flow; and sending, by the target access networkdevice to the terminal based on the trigger information, the data packetthat is of the at least one QoS flow and that is received from the corenetwork user plane device.

Optionally, the trigger information is an end marker packet, or thetrigger information is a control plane message between access networkdevices.

According to a seventh aspect, a data transmission apparatus isprovided, including units for performing the steps of the transmissionmethod according to any one of the first to the sixth aspects and theimplementations thereof.

In a design, the data transmission apparatus is a communications chip,and the communications chip may include an input circuit or interfacefor sending information or data, and an output circuit or interface forreceiving information or data.

In another design, the data transmission apparatus is a communicationsdevice, and the communications chip may include a transmitter forsending information or data, and a receiver for receiving information ordata.

According to an eighth aspect, a communications device is provided,including: a processor and a memory, where the memory is configured tostore a computer program, and the processor is configured to invoke thecomputer program from the memory and run the computer program, so thatthe communications apparatus performs the transmission method accordingto any one of the first to the sixth aspects and the possibleimplementations thereof.

Optionally, there are one or more processors and one or more memories.

Optionally, the memory may be integrated with the processor, or thememory is separate from the processor.

Optionally, the communications device further includes a transmitter anda receiver.

According to a ninth aspect, a computer program product is provided,where the computer program product includes a computer program (whichmay also be referred to as code or an instruction), and when thecomputer program runs, a computer performs the method according to anyone of the possible implementations of the first to the sixth aspects.

According to a tenth aspect, a computer readable medium is provided,where the computer readable medium stores a computer program (which mayalso be referred to as code or an instruction), and when the computerprogram runs on a computer, the computer performs the method accordingto any one of the possible implementations of the first and the secondaspects.

According to a ninth aspect, a chip system is provided, including amemory and processor, where the memory is configured to store a computerprogram, and the processor is configured to invoke the computer programfrom the memory and run the computer program, so that a communicationsdevice provided with the chip system performs the method according toany one of the possible implementations of the first to the sixthaspects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic architectural diagram of a communications systemaccording to an embodiment of this application;

FIG. 2 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 3 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 4 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 5 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 6 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 7 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 8 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 9 is a schematic flowchart of a transmission method according to anembodiment of this application;

FIG. 10 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 11 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 12 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 13 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 14 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 15 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 16 is a schematic flowchart of a transmission method according toan embodiment of this application;

FIG. 17 is a schematic diagram of a data transmission apparatusaccording to an embodiment of this application;

FIG. 18 is a schematic structural diagram of a terminal device accordingto this application;

FIG. 19 is a schematic diagram of a data transmission apparatusaccording to an embodiment of this application; and

FIG. 20 is a schematic structural diagram of a network device accordingto an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

In a next-generation communications system, an architecture based on aquality of service flow (QoS flow) is proposed, and the architecturesupports a guaranteed bit rate (GBR) QoS flow and a non-guaranteed bitrate (non-GBR) QoS flow.

Referring to FIG. 1, FIG. 1 shows a QoS architecture in 5G As shown inFIG. 1, for each terminal, a base station establishes one or more dataradio bearers (DRBs) for each PDU session of the terminal. The basestation maps data packets of different PDU sessions to different DRBs. AQoS flow is a finest granularity of QoS differentiation for a PDUsession. The PDU session is a connection between the terminal and anexternal data network to provide a packet data unit connectivityservice. Each PDU session has a unique identity, and the unique identityof the PDU session may be a PDU session identity. The QoS flow is a setof data packets, where data packets of a same QoS flow have same QoScharacteristics, and same packet forwarding and processing are performedon the data packets in a 3GPP network.

A packet processing mechanism on an air interface is defined based on aDRB in 5G. Packets served by a same DRB have a same packet processingmechanism on the air interface. The base station may establish aplurality of DRBs to meet different packet processing requirements ofQoS flows.

For example, for a downlink, the base station maps a downlink datapacket of a QoS flow to a DRB based on a QFI identity and acorresponding QoS profile on an NG-U (that is, an N3 interface). For anuplink, UE maps an uplink data packet of a QoS flow to a DRB based onmapping or reflective mapping that is from the QoS flow to the DRB andthat is configured by the base station.

The technical solutions of the embodiments of this application may beapplied to various communications systems, such as a Global System forMobile Communications (GSM) system, a Code Division Multiple Access(CDMA) system, a Wideband Code Division Multiple Access (WCDMA) system,a general packet radio service (GPRS), a Long Term Evolution (LTE)system, an LTE frequency division duplex (FDD) system, an LTE timedivision duplex (TDD) system, a Universal Mobile TelecommunicationsSystem (UMTS), a Worldwide Interoperability for Microwave Access (WiMAX)communications system, a future 5th generation (5G) system, and a NewRadio (NR) system.

The terminal in the embodiments of this application may be userequipment, an access terminal, a subscriber unit, a subscriber station,a mobile site, a mobile station, a remote station, a remote terminal, amobile device, a user terminal, a terminal device, a wirelesscommunications device, a user agent, or a user apparatus. The terminaldevice may alternatively be a cellular phone, a cordless phone, aSession Initiation Protocol (SIP) phone, a wireless local loop (WLL)station, a personal digital assistant (PDA), a handheld device having awireless communication function, a computing device, another processingdevice connected to a wireless modem, an in-vehicle device, a wearabledevice, a terminal device in a future 5G network, a terminal device in afuture evolved public land mobile network (PLMN), or the like. This isnot limited in the embodiments of this application.

The access network device or the base station in the embodiments of thisapplication may be a device for communicating with the terminal. Thenetwork device may be a base transceiver station (BTS) in the GlobalSystem for Mobile Communications (GSM) system or the Code DivisionMultiple Access (CDMA) system, or may be a NodeB (NB) in the WidebandCode Division Multiple Access (WCDMA) system, or may be an evolved NodeB(eNB or eNodeB) in the LTE system, or may be a radio controller in acloud radio access network (CRAN) scenario. Alternatively, the networkdevice may be a relay station, an access point, an in-vehicle device, awearable device, a network device in the future 5G network, a networkdevice in the future evolved PLMN, or the like. This is not limited inthe embodiments of this application.

A core network device in the embodiments of this application includes acore network control plane device and a core network user plane device.

A next-generation radio access network (NG-RAN) includes a gNB and/or anevolved eNB. The gNB provides an NR control plane and user planeprotocol stack that terminates at the terminal. The evolved eNB is anevolved LTE base station connected to a 5G core network. In descriptionof this application, the gNB and the evolved eNB may be collectivelyreferred to as a base station.

The gNB provides at least one of the following functions: accesscontrol, connection mobility management, radio bearer control,measurement configuration, dynamic resource allocation, and the like.

An Access and Mobility Management Function (AMF) provides at least oneof the following functions: non-access stratum (NAS) securitymanagement, access stratum (AS) security control, mobility management,terminal access verification, registration area management, slicesupport, session management function (SMF) selection, and the like.

A User Plane Function (UPF) provides at least one of the followingfunctions: anchor handover, data packet routing and forwarding, QoSmanagement, and the like.

An SMF provides at least one of the following functions: sessionmanagement, terminal IP address allocation and management, UPF selectionand control, and the like.

A next-generation core network control plane device includes but is notlimited to the AMF and the SMF. A next-generation core network userplane device includes but is not limited to the UPF.

An interface between the AMF and the NG-RAN is defined as an N2interface, and an interface between the UPF and the NG-RAN is defined asan N3 interface. An interface between gNBs is defined as an Xninterface.

Start-to-send information and trigger information in the embodiments ofthis application are interchangeable with each other. An SN may be asecondary base station, and an MN may be a master base station.

In the following description, the access network device and the basestation are interchangeable with each other.

FIG. 2 is a schematic flowchart of a transmission method according tothis application. The method shown in FIG. 2 may be applied to a processin which at least one QoS flow (denoted as a QoS flow #1) in a first PDUsession of a terminal is transferred to a target base station. Forexample, in a dual connectivity scenario, the QoS flow #1 in the firstPDU session of the terminal is transferred to the target base station (amaster base station or a secondary base station base station), and otherQoS flow in the first PDU session remains in a source base station (asecondary base station or a master base station). The transmissionmethod in this embodiment of this application is described below indetail with reference to FIG. 2.

S210. A first base station sends a first request message to a corenetwork device.

The first request message includes an identity of the first PDU sessionand an identity of the QoS flow #1. The first request message is used torequest to change a user plane route of the QoS flow #1 to a second basestation.

It should be understood that the first base station may be the masterbase station in the dual connectivity scenario. When the master basestation is the source base station, the secondary base station is thesecond base station. That is, the first base station and the second basestation are different base stations. When the master base station is thetarget base station, the master base station is the second base station.That is, the first base station and the second base station are a samebase station.

It should further be understood that the core network device is a devicecompatible with a function of a core network user plane device and afunction of a core network control plane device.

Optionally, the first request message may be a path switch requestmessage. This may be more compatible with the prior art.

S220. The core network device sends an end marker packet based on thefirst request message.

Specifically, if a core network user plane consents to change the userplane route of the QoS flow #1 to the second base station, the endmarker packet is sent to the second base station. The end marker packetincludes the identity of the QoS flow #1. The end marker packetindicates that the core network device stops sending a data packet ofthe QoS flow #1 in a source data tunnel of the first PDU session. Inother words, the end marker packet indicates that the core network userplane no longer sends the data packet of the QoS flow #1 in the sourcedata tunnel.

The end marker packet may be an empty data packet. In addition, anencapsulation header of the empty data packet may carry an end marker.For example, the end marker may be carried in a General Packet RadioService tunneling protocol user plane (GTPU) header or extension header.The encapsulation header of the empty data packet may carry the identityof the QoS flow #1.

Further, the core network device may send several end marker packets, toincrease a success rate of correctly receiving the end marker packet bythe source base station.

It should be noted that, if the first base station is the source basestation of the QoS flow #1, step S220 is specifically: the core networkdevice sends an end marker packet to the first base station based on thefirst request message. If the first base station is the target basestation of the QoS flow #1, the first base station and the second basestation are the same base station, and step S220 is specifically: thecore network device sends the end marker packet to the second basestation or the first base station based on the first request message.

According to the transmission method in this embodiment of thisapplication, the core network device sends an end marker packet based ona first request message sent by an access network device, so as toindicate, to the access network device, that a core network user planedevice terminates downlink transmission of a QoS flow in a source datatunnel. In this way, switching of downlink transmission at a level orgranularity of a QoS flow can be implemented, and thereby systemflexibility can be improved.

FIG. 3 is a schematic flowchart of another transmission method accordingto this application. The method shown in FIG. 3 may be applied to aprocess in which at least one QoS flow (denoted as a QoS flow #1) or allQoS flows in a first PDU session of a terminal are transferred to atarget base station. For example, during switching, all the QoS flows inthe first PDU session of the terminal are transferred to the target basestation; or all the QoS flows in the first PDU session are to betransferred to the target base station, but only a QoS flow #1 isaccepted successfully by the target base station. For another example,in a dual connectivity scenario, the QoS flow #1 in the first PDUsession of the terminal is transferred to the target base station (amaster base station or a secondary base station), and other QoS flow inthe first PDU session remains in a source base station (a secondary basestation or a secondary base station).

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 3.

S301. An access network device sends a request message #1 to a corenetwork control plane device. The request message #1 includes anidentity of the first PDU session.

Optionally, the route changing request message may further include anidentity of the QoS flow #1.

Specifically, the access network device may be a source base station, ormay be a target base station. When the route changing request message 1is sent by the source bases station, the request message #1 furtherincludes the identity of the QoS flow #1. The request message #1 is usedto request to change a use plane route of the QoS flow #1 in the firstPDU session to the target base station. It should be understood that thesource base station herein is the master base station or the secondarybase station in the dual connectivity scenario. Correspondingly, thetarget base station herein is the secondary base station or the masterbase station in the dual connectivity scenario. When the request message#1 is sent by the target base station, if the request message #1includes only the identity of the first PDU session, the route changingrequest message is used to request to switch a data tunnel of the firstPDU session towards the target base station.

Further, the request message #1 may further include independentindication information (denoted as indication information #1A). Theindication information #1A is used to indicate whether the data tunnelof the first PDU session is switched or a route of the QoS flow #ischanged.

It should be understood that, in all embodiments described in thisapplication, switching of the data tunnel of the first PDU session meansthat the data tunnel corresponding to the first PDU session between acore network user plane device and the source base station is no longerused after the data tunnel switching is completed. After the data tunnelswitching is completed, the core network user plane device and theterminal use a data tunnel that corresponds to the first PDU session andthat is between the core network user plane device and the target basestation for data transmission. Changing of the user plane route of theQoS flow #1 means that the QoS flow #1 whose route is changed istransmitted over a data tunnel that corresponds to the QoS flow #1 andthat is between the core network user plane device and the target basestation, and that a QoS flow whose route is unchanged in the first PDUsession continues to be transmitted over a data tunnel that correspondsto the first PDU session and that is between the core network user planedevice and the source base station.

Optionally, the request message #1 may be a path switch request message.This may be more compatible with the prior art.

S302. The core network control plane device sends a request message #2to a core network user plane device.

The request message #2 may be the same as or may be different from therequest message #1. When the request message #2 is different from therequest message #1, the request message #2 is generated by the corenetwork control plane device based on the request message #1, and therequest message #2 includes the identity of the first PDU session.Optionally, the request message #2 may further include the identity ofthe QoS flow #1.

S303. The core network user plane device changes a route of a datapacket and sends an end marker packet to a source base station.

The end marker packet includes the ID of the QoS flow #1. The end markerpacket is used to indicate, to the source base station, that the corenetwork user plane device no longer sends a data packet of the QoS flow#1 to the source base station.

Specifically, if the request message #1 includes only the ID of thefirst PDU session or further includes the indication information #1, thecore network user plane device sends the end marker packet to the sourcebase station. Alternatively, the route changing request message 1further includes the ID of the QoS flow #1 or further includes the ID ofthe QoS flow #1 and the indication information #1, and the core networkuser plane device sends the end marker packet to the source basestation.

Further, the core network user plane device may send several end markerpackets, to increase a success rate of correctly receiving the endmarker packet by the source base station.

The end marker packet may be an empty data packet (namely, the endmarker packet does not contain user data). In addition, an encapsulationheader of the empty data packet may carry an end marker. For example,the end marker may be carried in a GTPU header or extension header. Theencapsulation header of the empty data packet may carry the identity ofthe QoS flow #1.

Optionally, a format of the end marker packet in step S303 may include aplurality of QoS flow fields, and the plurality of QoS flow fields arein one-to-one correspondence with a plurality of QoSs. In thisembodiment of this application, the end marker packet sent in step S303may alternatively be a dedicated end marker packet. In this case, theend marker packet may carry the ID of the QoS flow #1, or may not carrythe ID of the QoS flow #1.

For example, if the request message #1 is used to request to switch thedata tunnel of the first PDU session towards the target base station,the core network user plane device may send an end marker packet #1 tothe source base station. The end marker packet #1 is used to indicatethat the core network user plane device no longer sends a data packet ofany QoS flow in the first PDU session to the source base station.Further, the end marker packet #1 may further carry indicationinformation (denoted as indication information #1B), and the indicationinformation #1B is used to indicate that the end marker packet #1 isspecific to all QoS flows in the first PDU session.

For another example, if the request message #1 is used to request tochange the data tunnel of the QoS flow #1 towards the target basestation, the core network user plane device may send an end markerpacket #2 to the source base station. The end marker packet #2 is usedto indicate that the core network user plane device no longer sends thedata packet of the QoS flow #1 to the source base station. Further, theend marker packet #2 may further carry indication information (denotedas indication information #1C), and the indication information #1C isused to indicate that the end marker packet #2 is specific to a QoSflow.

It should be understood that the end marker packet #1 and the end markerpacket #2 are data packets having different structures.

Further, when QoS flow route changing is performed for the first time,for example, when route changing for the QoS flow #1 is performed, theaccess network device may notify the core network control plane deviceof an ID of the target base station and a routing address that is in thetarget base station and that is of a data tunnel of a PDU session towhich the QoS flow whose route is changed belongs. When route changingfor a QoS flow in the same PDU session is performed subsequently, theaccess network device may notify the core network control plane deviceof only the identity of the target base station or a target routingaddress.

The foregoing routing address includes a transport layer address and aGeneral Packet Radio Service tunneling protocol tunnel endpointidentifier (GPRS Tunnelling Protocol Tunnel Endpoint Identifier, GTP TEid).

Further, the end marker packet may further carry indication informationthat is used to indicate that the end marker packet is specific to a QoSflow, or may be used to indicate that the end marker is specific to aQoS flow group. For example, if the base station requests route changingfor a group of QoS flows, the core network user plane device may set anend marker packet, to indicate the end of sending data packets of theQoS flow group in the source data tunnel of the PDU session.

According to the transmission method in this embodiment of thisapplication, the core network user plane device sends the end markerpacket based on the request message #1 sent by the access network deviceby using the core network control plane device, so as to indicate, tothe source base station, that the core network user plane deviceterminates downlink transmission of the at least one QoS flow indownlink transmission to the source base station. In this way, switchingof downlink transmission at a level or granularity of a QoS flow can beimplemented, and thereby system flexibility can be improved.

FIG. 4 is a schematic flowchart of another transmission method accordingto this application. A core network user plane device in FIG. 4 may be aUPF, and a core network control plane device may be an SMF and/or anAMF. This is not limited in this embodiment of this application.

The method shown in FIG. 4 may be applied to a process in which at leastone QoS flow (denoted as a QoS flow #1) or all QoS flows in a first PDUsession of a terminal are transferred to a target base station. Forexample, during switching, all the QoS flows in the first PDU session ofthe terminal are transferred to the target base station; or all the QoSflows in the first PDU session are to be transferred to the target basestation, but only the QoS flow #1 is accepted successfully by the targetbase station. For another example, in a dual connectivity process, theQoS flow #1 in the first PDU session of the terminal is transferred tothe target base station (a master base station or a secondary basestation), and a remaining QoS flow in the first PDU session remains in asource base station (a master base station or a secondary base station).

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 4.

S401. An access network device sends a first request message to the corenetwork control plane device.

The first request message is used for requesting the core network userplane device by the core network control plane device to change a userplane route to the target base station.

It should be understood that the access network device may be the sourcebase station, or may be the target base station. When the first requestmessage is sent by the source base station, the first request message isused to request to change a user plane route of at least one QoS flow(denoted as the QoS flow #1) in a PDU session (denoted as the first PDUsession) to the target base station. It should be understood that thesource base station herein is the master base station or the secondarybase station in a multi-connectivity scenario. Correspondingly, thetarget base station herein is the secondary base station or the masterbase station in the multi-connectivity scenario. When the route changingrequest message is sent by the target base station, the route changingrequest message is used to request to switch a data tunnel of the firstPDU session towards the target base station.

S402. The core network control plane device sends a second requestmessage to the core network user plane device based on the first requestmessage, and notifies the core network user plane device to change aroute by using the second request message.

S403. The core network user plane device sends an end marker packet tothe source base station.

S404. When the source base station determines that the first requestmessage corresponding to the end marker packet is a route changingrequest message, the source base station may determine that the endmarker packet indicates that the core network user plane deviceterminates transmission of data packets of the QoS flow #1 in a sourcedata tunnel of the first PDU session.

Optionally, the method may further include the following:

when the source base station determines that the first request messagecorresponding to the end marker packet is a path switch request message,the source base station may determine that the end marker packetindicates that the core network user plane device terminatestransmission of data packets of all QoS flows in the source data tunnelof the first PDU session.

Specifically, the source base station may determine, based on a type ofthe message sent by the source base station, whether the end markerpacket sent by the core network user plane device is used to end the QoSflow #1 or end the entire first PDU session. If the first requestmessage is the route changing request message, the end marker packetindicates that the core network user plane device terminates thetransmission of the data packet of the QoS flow #1 in the source datatunnel of the first PDU session. If the first request message is thepath switch request message, the end marker packet indicates that thecore network user plane device terminates the transmission of datapackets of all the QoS flows in the source data tunnel of the first PDUsession.

When the access network device is the master base station, the masterbase station is the target base station, and the secondary base stationis the source base station, the source base station determines, based onmessage exchange with the target base station, a type of the firstrequest message sent by the target base station to the core networkcontrol plane device.

For example, if the source base station sends a handover request messageto the target base station, the type of the first request message sentby the target base station to the core network control plane device isthe path switch request message.

If the source base station sends, to the target base station, a requestmessage for transfer of some QoS flows of the terminal to the targetbase station, the type of the first request message sent by the targetbase station to the core network control plane device is the routechanging request message.

Further, the source base station may determine, based on differentscenarios, whether the end marker packet corresponds to a QoS flow or aPDU session. For example, in a handover scenario, it is determined thatthe end marker packet indicates that the core network user plane deviceterminates the transmission of the data packets of all the QoS flows inthe source data tunnel of the first PDU session. In the dualconnectivity scenario, the end marker packet indicates that the corenetwork user plane device terminates the transmission of the data packetof the QoS flow #1 in the source data tunnel of the first PDU session.

Further, the core network user plane device may send several end markerpackets, to increase a success rate of correctly receiving the endmarker packet by the source base station.

The end marker packet may be an empty data packet. In addition, anencapsulation header of the empty data packet may carry an end marker.For example, the end marker may be carried in a GTPU header or extensionheader.

According to the transmission method in this embodiment of thisapplication, when the source base station or the target base stationrequests, by using the first request message, the core network userplane device to end transmission of data packets of one or more QoSflows in the source data tunnel, the core network user plane device mayuse the end marker packet to indicate, to the source base station, thatthe core network user plane device terminates the transmission of thedata packets in the entire PDU session in the source data tunnel. Inthis way, switching of downlink transmission at a level or granularityof a QoS flow can be implemented, and thereby system flexibility can beimproved.

In addition, when the target base station requests, by using the pathswitch request message, to end the transmission of the data packets ofall the QoS flows in the entire PDU session in the source data tunnel,the core network user plane device may also use an end marker packethaving a same format to indicate, to the source base station, that thecore network user plane device terminates the transmission of the datapackets in the entire PDU session in the source data tunnel. The corenetwork user plane device uses the end marker packet having a uniformformat, and therefore processing complexity of the end marker packet bythe core network user plane device and the source base station can bereduced.

FIG. 5 is a schematic flowchart of another transmission method accordingto this application. A core network user plane device in FIG. 5 may be aUPF, and a core network control plane device may be an SMF and/or anAMF.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 5.

S501. A source base station receives an end marker packet sent by aterminal or the core network user plane device, where the end markerpacket includes an identity of a first PDU session and an identity of atleast one QoS flow (denoted as a QoS flow #1).

S502. The source base station releases or terminates, based on the endmarker packet, a resource corresponding to the QoS flow #1.

Optionally, the source base station releases a parameter of the QoS flow#1 in a context of the terminal.

Specifically, the terminal or the core network user plane device mayautonomously determine to terminate transmission of the QoS flow #1. Forexample, when the terminal determines to terminate uplink transmissionof the QoS flow #1, the terminal sends the end marker packet, to notifythe source base station of the end of the uplink transmission of the QoSflow #1. After sending the end marker packet, the terminal no longersends a data packet of the QoS flow #1 to the source base station. Foranother example, when the core network user plane device determines toterminate downlink transmission of the QoS flow #1, the core networkuser plane device sends the end marker packet, to notify the source basestation of the end of the downlink transmission of the QoS flow #1.After sending the end marker packet, the core network user plane deviceno longer sends a data packet of the QoS flow #1 to the source basestation. After receiving the end marker packet, the source base stationno longer sends a data packet of the QoS flow #1 to the terminal.

Optionally, the terminal or the core network user plane device may sendseveral end marker packets, to increase a success rate of correctlyreceiving the end marker packet by the source base station.

The end marker packet may be an empty data packet. In addition, anencapsulation header of the empty data packet may carry an end marker.For example, the end marker may be carried in a GTPU header or extensionheader. The encapsulation header of the empty data packet may carry theID of the QoS flow #1.

According to the transmission method in this embodiment of thisapplication, the terminal or the core network user plane device may sendthe end marker packet including the ID of a QoS flow, to terminate thetransmission of the QoS flow #1.

After receiving the end marker packet, the source base station mayrelease or terminate the resource allocated to the QoS flow #1.

Further, the source base station may release a QoS parameter of the QoSflow #1 in the context of the terminal. The QoS parameter includes butis not limited to indicator parameters such as a latency, a packet lossrate, a priority, and a rate. In this way, system resources are saved.

Transmission methods applied to an inter-system handover process aredescribed below in detail with reference to FIG. 6, FIG. 7, and FIG. 8.Specifically, the transmission methods shown in FIG. 6, FIG. 7, and FIG.8 may be used in a process of forwarding of a data packet or data.

The data forwarding or the data packet forwarding means that a sourcebase station transmits, to a target base station, a data packet receivedfrom a core network user plane device or a terminal, and the target basestation sends the data packet received from the source base station tothe terminal or the core network user plane device.

In the following description, a first core network control plane devicemay be an AMF and/or an SMF, a second core network control plane devicemay be an MME, a first core network user plane device may be a UPF, anda second core network user plane device may be an S-GW.

FIG. 6 is a schematic flowchart of a transmission method according tothis application. The transmission method in this embodiment of thisapplication is described below in detail with reference to FIG. 6.

S601. A source base station sends a first request message to a firstcore network control plane device.

The first request message includes a forwarding indication, and theforwarding indication is used to instruct a first core network userplane device to send a forwarded data packet of a first PDU session to atarget base station.

Optionally, the first request message may further include an ID of atleast one QoS flow (denoted as a QoS flow #1). Based on an indication ofthe ID of the QoS flow #1, the source base station requests to performtransmission of the to-be-forward data packet by using the QoS flow #1.

It should be noted that the to-be-forward data packet may be, all datapackets for which no reception acknowledgement is received from aterminal, or all data packets that are not yet sent to the terminal, indata packets received by the source base station from the first corenetwork user plane device (for example, a UPF).

S602. The first core network control plane device sends a first responsemessage to the source base station based on the first request message.

The first response message includes an identity of at least one firstEPS bearer corresponding to the first PDU session and the forwardingindication.

S603. The source base station generates transparent containerinformation from the source base station to a target base station basedon the first response message.

The transparent container information may include radio relatedinformation of the source base station, for example, an E-RAB ID list,E-RAB UE history information corresponding to each E-RAB ID, and aforwarding indication. An E-RAB is in one-to-one correspondence with anEPS Bearer. It should be understood that the forwarding indicationherein indicates that the E-RAB has data to be forwarded.

S604. The source base station sends a handover request message to thecore network control plane device, where the handover request messageincludes the transparent container information.

Then, nodes, for example, the source base station and the target basestation, may perform a handover process according to the prior art.Details are not described herein in this embodiment of this application.In this way, the source base station may indicate, to the target basestation, which E-RAB has downlink data to be forwarded.

FIG. 7 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 7 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 7 may also be performed. In addition, steps in FIG. 7may be performed in an order different from that shown in FIG. 7, andnot all operations in FIG. 7 may be performed.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 7.

S701. A source base station transmits data received from the first corenetwork user plane device (to-be-forward-transmitted data) and a firstend marker packet to a first core network user plane device.

The first end marker packet is received by the source base station fromthe first core network user plane device. The first end marker packetmay be an empty data packet. In addition, an encapsulation header of theempty data packet carries an end marker. For example, the end marker iscarried in a GTPU header or extension header.

Specifically, a data tunnel for data forwarding may be establishedbetween the source base station and the first core network user planedevice. The data forwarding tunnel is established per a PDU session,that is, a data tunnel for forwarding data is established for each PDUsession. A data tunnel established per a PDU session and correspondingto a first PDU session may be denoted as a data tunnel #1, and thesource base station may forward the data packet and the first end markerpacket to the first core network user plane device over the data tunnel#1.

The first end marker packet may be set according to a PDU session, toindicate the end of sending packets in the session; or may be setaccording to a QoS flow, to indicate the end of sending packets of theQoS flow.

S702. The first core network user plane device generates a second endmarker packet based on the first end marker packet and a correspondencebetween a first session and a first EPS bearer, where the second endmarker packet carries an identity of the first EPS bearer.

S703. The first core network user plane device sends the forwarded datapacket and the second end marker packet to a second core network userplane device.

Specifically, a data tunnel for data forwarding is established betweenthe first core network user plane device and the second core networkuser plane device and between the second core network user plane deviceand a target base station according to an EPS bearer. A data tunnelestablished according to an EPS bearer and corresponding to the firstPDU session may be denoted as a data tunnel #2, and then the first corenetwork user plane device may send the forwarded data packet and thesecond end marker packet to the second core network user plane deviceover the data tunnel #2.

S704. The second core network user plane device sends the forwarded datapacket and the second end marker packet to the target base station.

S705. After sending the forwarded data packet to a terminal based on thesecond end marker, the target base station sends a data packet receivedfrom the second core network user plane device to the terminal.

Specifically, the target base station first sends the received forwardeddata packet, and after determining, based on the second end markerpacket, that the forwarded data packet on the EPS bearer has been sent,sends the data packet (that is, a fresh data packet) received from thesecond core network user plane device. In this way, in-ordertransmission of data packets on the EPS bearer can be ensured.

In this embodiment of this application, after the target base stationreceives and detects the second end marker packet, the second end markerpacket may be discarded. Further, the target base station may release aresource of the data tunnel #2.

According to the transmission method in this embodiment of thisapplication, the first core network user plane device sets and sends thesecond end marker packet corresponding to the EPS bearer, so that thetarget base station can first send, based on the end marker packet, theforwarded data packet received from the source base station, and thensends the fresh data packet received from the second core network userplane device, thereby ensuring the in-order transmission of the datapackets on the EPS bearer.

FIG. 8 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 8 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 8 may also be performed. In addition, steps in FIG. 8may be performed in an order different from that shown in FIG. 8, andnot all the operations in FIG. 8 may be performed.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 8.

S801. A source base station transmits data received from the first corenetwork user plane device and a first end marker packet to a first corenetwork user plane device.

The first end marker packet is received by the source base station fromthe first core network user plane device, and the first end markerpacket may be an empty data packet. In addition, an encapsulation headerof the empty data packet may carry an end marker. For example, the endmarker may be carried in a GTPU header or extension header.

Specifically, a data tunnel for data forwarding may be establishedbetween the source base station and the first core network user planedevice. The data forwarding tunnel is established according to a PDUsession, that is, a data tunnel for transmitting a to-be-forward-datapacket is established for each PDU session. A data tunnel establishedaccording to a PDU session and corresponding to a first PDU session maybe denoted as a data tunnel #1, and then the source base station maysend the to-be-forward-data packet and the first end marker packet tothe first core network user plane device by using the data tunnel #1.

S802. The first core network user plane device successively sends theforwarded data and a fresh data packet to a second core network userplane device based on the first end marker packet.

Specifically, a data tunnel is established between the first corenetwork user plane device and the second core network user plane deviceand between the second core network user plane device and a target basestation according to an EPS bearer, to transmit forwarded downlink data(that is, a forwarded data packet) of the source base station that isreceived from the first core network user plane device and the freshdata packet. The data tunnel herein established according to the EPSbearer may be denoted as a data tunnel #3. The first core network userplane device determines, based on the first end marker packet, that theforwarded data has been sent by using the data tunnel #3, and then thefirst end marker packet is discarded. Then the fresh data packet is sentby using the data tunnel #3.

Further, an encapsulation header of the forwarded data may carry anidentity of a QoS flow, and the first core network user plane devicedetermines the data tunnel #3 based on the identity of the QoS flow. Forexample, a data tunnel corresponding to the EPS bearer is indexed basedon a correspondence between the QoS flow and the EPS bearer.

S803. The second core network user plane device successively sends theforwarded data packet and the fresh data packet to a target basestation.

S804. The target base station sends a downlink data packet received fromthe second core network user plane device to a terminal. The downlinkdata packet includes the forwarded data packet and the fresh datapacket.

According to the method in this embodiment of this application, thesource base station sends the to-be-forward-data packet to the firstcore network user plane device, and the first core network user planedevice first sends the forwarded data packet received from the sourcebase station and then sends the fresh data packet, thereby ensuringin-order transmission of data packets on the EPS bearer. In addition, atunnel for forwarding of downlink data does not need to be establishedbetween the first core network user plane device and the second corenetwork user plane device and between the second core network user planedevice and the target base station, thereby reducing overheads. Thetarget base station does not need to differentiate between the forwardeddata and the fresh data packet.

Data forwarding in an inter-system handover is described above, andtransmission methods for data forwarding that are applied to theinter-system handover process are described below in detail withreference to FIG. 9, FIG. 10, and FIG. 11.

First, it should be noted that, in the following description withreference to FIG. 9, FIG. 10, and FIG. 11, a data packet that is of afirst PDU session and that needs to be sent by a source base station toa target base station is a data packet that needs to be forwarded indata packets of the first PDU session. The data packet that needs to beforwarded in the data packets of the first PDU session may be any one ofthe following:

(1) all data packets for which no reception acknowledgement is receivedfrom a terminal, and/or all data packets that are not yet sent to theterminal, in data packets that are of the first PDU session and that arereceived by the source base station from a core network user planedevice;

(2) a data packet cached in a first SDAP entity of the source basestation, that is, a SDAP SDU; or

(3) a data packet cached in a first SDAP entity of the source basestation and a data packet that is not successfully sent by a PDCPentity.

It should be understood that the first SDAP entity corresponds to thefirst PDU session. The data packet for which no reception confirmationis received from the terminal, the data packet that is not yet sent tothe terminal, and the data packet that is not successfully sent by thePDCP entity are all cached in the PDCP entity. Therefore, the datapacket that is of the first PDU session and that needs to be sent by thesource base station to the target base station is the data packet cachedin the first SDAP entity and/or the data packet cached in the PDCPentity. Specifically, if there is a cached data packet in the first SDAPentity, the data packet that is of the first PDU session and that needsto be sent by the source base station to the target base station is thedata packet cached in the first SDAP entity and the data packet cachedin the PDCP entity; or if there is no cached data packet in the firstSDAP entity, the data packet that is of the first PDU session and thatneeds to be sent by the source base station to the target base stationis the data packet cached in the PDCP entity.

FIG. 9 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 9 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 9 may also be performed. In addition, steps in FIG. 9may be performed in an order different from that shown in FIG. 9, andnot all the operations in FIG. 9 may be performed.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 9.

S901. A source base station sends a first proportion of data packets ofa first Packet Data Convergence Protocol (PDCP) entity to a target basestation by using a data tunnel between the first PDCP entity and asecond PDCP entity of the target base station.

The first proportion of data packets are data packets of a first QoSflow (denoted as a QoS flow #1) in the first protocol data unit (PDU)session. The first PDU session includes at least one QoS flow. The atleast one QoS flow is in one-to-one correspondence with at least onePDCP entity. The at least one QoS flow includes the first QoS flow. Theat least one PDCP entity includes the first PDCP entity. The first PDCPentity corresponds to the first QoS flow. The first QoS flow is any oneof the at least one QoS flow.

S902. The source base station sends first indication information to thetarget base station. The first indication information is used toindicate that the first proportion of data packets of the first PDCPentity have been sent.

S903. After determining, based on the first indication information, thatall data packets of the first proportion of data packets have been sentto a terminal, the target base station sends a data packet received froma SDAP entity of the target base station to the terminal.

Optionally, the first indication information includes a largest PDCPsequence number in PDCP sequence numbers carried by all data packets inthe first proportion of data packets; or

the first indication information includes a next to-be-allocated PDCPsequence number; or

the first indication information is an end marker packet generated bythe first PDCP entity.

Optionally, before the source base station sends the first proportion ofdata packets in the first PDCP entity to the second PDCP entity of thetarget base station, the method further includes:

receiving, by the first PDCP entity, second indication information sentby the first SDAP entity of the source base station, where the secondindication information is used to indicate that the first SDAP entitystops sending data packets of the first QoS flow to the first PDCPentity, the data packets of the first QoS flow that are sent by thefirst SDAP entity to the first PDCP entity are the first proportion ofdata packets, and the first SDAP entity corresponds to the first PDUsession.

Optionally, the second indication information is sent by the SDAP entitybased on an end marker packet received from a core network user planedevice.

FIG. 10 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 10 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 10 may also be performed. In addition, steps in FIG.10 may be performed in an order different from that shown in FIG. 10,and not all the operations in FIG. 10 may be performed.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 10.

S1001. A first SDAP entity of a source base station sends firstindication information to a first PDCP entity of the source basestation.

A first PDU session includes at least one QoS flow, and the at least oneQoS flow corresponds to a PDCP entity. A first PDCP in the at least onePDCP entity corresponds to a first QoS flow (denoted as a QoS flow #1)in the first PDU session, and the QoS flow #1 may be any flow in thefirst PDU session. Therefore, without loss of generality, if the atleast one QoS flow included in the first PDU session further includesother QoS flows (denoted as a QoS flow #2 to a QoS flow #R, where R isan integer greater than or equal to 2) in addition to the QoS flow #1,and a data packet that needs to be forwarded exists in the QoS flow #2to the QoS flow #R, other PDCP entities that are in the at least onePDCP entity and that are in one-to-one correspondence with the QoS flow#2 to the QoS flow #R may perform forwarding of data packets of the QoSflow #2 to the QoS flow #R with reference to the operation of the firstPDCP entity.

Specifically, if there is no cached data packet in the first SDAP entityin the source base station, or there is a cached data packet but thefirst SDAP entity currently stops sending a data packet to the firstPDCP entity, the first SDAP entity sends the first indicationinformation to the first PDCP entity. The first indication informationis used to indicate that the first SDAP entity no longer sends a datapacket of the QoS flow #1 to the first PDCP entity. The first PDCPentity may determine, based on the first indication information, thelast data packet sent by the first SDAP entity and received by the firstPDCP entity. Optionally, the first indication information may be an endmarker packet, and a SDAP header of the end marker packet carries theend marker. The end marker packet may be an empty data packet.

S1002. The first PDCP entity sends data packets (denoted as a datapacket #1 to a data packet #i, where i is an integer greater than orequal to 1) that are of a QoS flow #1 and that are cached in the firstPDCP entity to a second PDCP entity of a target base station by using adata tunnel (denoted as a data tunnel #1) between the first PDCP entityand the second PDCP entity, where the second PDCP entity corresponds tothe QoS flow #1.

It should be understood that the first PDCP entity and the second PDCPentity may use the prior art or a new method to be proposed in thefuture to establish the data tunnel #1, and this is not limited in thisexample of this application.

S1003. The source base station sends second indication information tothe target base station based on the first indication information.

The second indication information is used to indicate that the firstPDCP entity has sent all the data packets, that is, the data packet #1to the data packet #i, that are of the QoS flow #1 and that are cachedin the first PDCP entity.

Specifically, the source base station may determine, based on the firstindication information, for example, the end marker packet, the lastdata packet, that is, the data packet #i, that is sent by the first SDAPentity and that is received by the source base station. Therefore, aftersending the data packet #i, the source base station sends the secondindication information to the target base station, and notifies, byusing the second indication information, the target base station thatthe source base station has sent all the cached data packets in thefirst PDCP entity and no longer sends a data packet to the second PDCPentity.

Optionally, the second indication information may be sent by using amessage between Xn interfaces, for example, sent by using an SN statustransfer (SN STATUS TRANSFER) message.

Further, the first PDCP entity may allocate PDCP SNs to all the datapackets cached in the first PDCP entity. In this case, the secondindication information may be a largest PDCP sequence number in the datapackets cached in the first PDCP entity, that is, a PDCP sequence numberof the data packet #i. Alternatively, the second indication informationmay be a next to-be-allocated largest sequence number.

Optionally, the second indication information may be a second end markerpacket, and the second end marker packet carries an end marker.

Specifically, if the data packets cached in the first PDCP entityinclude a data packet to which a PDCP SN is allocated and a data packetto which no PDCP SN is allocated, the source base station may set thesecond end marker packet after determining, based on the firstindication information, the last data packet (that is, the data packet#i) in the data packets cached in the first PDCP entity, and send thesecond end marker packet after having sent the data packet #i to thesecond PDCP entity. The second end marker packet may be an empty datapacket, and a GTPU header or a GTPU extension header of the end markerpacket may carry the end marker.

Further, the target base station may release a resource of the datatunnel #1 after receiving the second indication information.

S1004. The second PDCP entity sends the data packet #1 to the datapacket #i to a terminal.

Optionally, if there is a data packet cached in the first SDAP entity,the method may further include the following steps.

S1005. The first SDAP entity sends a first end marker packet and datapackets that are of a first PDU session and that are cached in the firstSDAP entity to the second SDAP entity of the target base station byusing a data tunnel (denoted as a data tunnel #2) between the first PDCPentity and the second SDAP entity.

For ease of understanding and description, the data packets that are ofthe first PDU session and that are cached in the first SDAP entity aredenoted below as a data packet (i+1) to a data packet M, where M is aninteger greater than or equal to 2.

Specifically, the first SDAP entity sends the data packet (i+1) to thedata packet M by using the data tunnel #2, and sends the first endmarker packet after sending the data packet M. The first end markerpacket is received by the first SDAP entity from a core network userplane device. The first end marker packet includes an end marker, andthe first end marker packet is used to indicate that the first SDAPentity has sent all the data packets that are of the first PDU sessionand that are cached in the first SDAP entity. The second SDAP entitycorresponds to the first PDU session. After receiving the first endmarker packet, the second SDAP entity may determine that the first SDAPentity has sent all the data packets cached in the first SDAP entity.

S1006. After determining, based on the second indication information,that all the data packet #1 to the data packet #i have been sent, thesecond PDCP entity sends the data packets received from the second SDAPentity, where the second SDAP entity corresponds to the first PDUsession.

Specifically, the second PDCP entity may determine, based on the secondindication information, that all the data packets received from thefirst PDCP entity have been sent to the terminal. Then the second PDCPentity sends the data packets that are of the first PDU session and thatare received from the second SDAP. In this way, it can be ensured that,after all data packets that need to be forwarded have been sent, datapackets after the forwarded data packets are sent, so as to avoidout-of-order of the data packets of the first PDU session.

Referring to step S1005, if the first SDAP entity sends the data packet(i+1) to the data packet M by using the data tunnel #2, in step S1006,after the second PDCP entity determines, based on the second indicationinformation, that all the data packets received from the first PDCPentity have been sent to the terminal, the second PDCP entity sends thedata packet (i+1) to the data packet M that are received from the secondSDAP. After having sent all the data packets before the first end markerpacket, the second SDAP starts to send the data packets that are of theQoS flow #1 and that are received from the core network user plane tothe second PDCP entity. In this way, it can be ensured that, after allthe received to-be-transmitted data packets have been sent, the datapackets after the to-be-transmitted data packets are sent, so as toavoid out-of-order of the data packets of the first PDU session.

In this embodiment of this application, if a mapping relationshipbetween a QoS flow and a DRB in the target base station is inconsistentwith that in the source base station, for example, the QoS flow #1 ismapped to a DRB #1 (corresponding to the first PDCP entity) in thesource base station, while the QoS flow #1 is mapped to a DRB #2(corresponding to the second PDCP entity) in the target base station,after the second PDCP entity and PDCP entities corresponding to the QoSflow #2 to the QoS flow #R in the target base station have sent all theforwarded data packets of the first PDU session, the second SDAP entitysends data packets to the second PDCP and the PDCP entitiescorresponding to the QoS flow #2 to the QoS flow #R in the target basestation. In this way, in-order transmission of the data packets of QoSflows can be ensured.

FIG. 11 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 11 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 11 may also be performed. In addition, steps in FIG.11 may be performed in an order different from that shown in FIG. 11,and not all the operations in FIG. 11 may be performed.

The transmission method in this embodiment of this application isdescribed below in detail with reference to FIG. 11.

S1101. A first SDAP entity of a source base station sends a data packetthat is of a first PDU session and that is cached in the first SDAPentity to a second SDAP entity of a target base station by using a datatunnel (denoted as a data tunnel #3) between the first SDAP entity andthe second SDAP entity.

Optionally, the method may further include the following steps.

S1102. At least one PDCP entity of the source base station sends a datapacket that is of the first PDU session and that is cached in the atleast one PDCP entity to the second SDAP entity by using the data tunnel#3.

The at least one PDCP entity includes one or more PDCP entities, the oneor more PDCP entities are in one-to-one correspondence with one or moreQoS flows in the first PDU session, and the at least one PDCP entity maycache all data packets that need to be forwarded in data packets of thefirst PDU session.

Specifically, when there is no data packet cached in the at least onePDCP entity, the first SDAP sends the data packet that is of the firstPDU session and that is cached in the first SDAP entity to the secondSDAP entity by using the data tunnel #3. When there is a data packetcached in the at least one PDCP entity, the first SDAP and the at leastone PDCP entity send the data packet that is of the first PDU sessionand that is cached in the first SDAP entity and the data packet that isof the first PDU and that is cached in the at least one PDCP entity tothe second SDAP entity by using the data tunnel #3.

S1103. The source base station sends first indication information to thetarget base station.

Optionally, the first indication information may be an end markerpacket. The source base station sends second indication information tothe target base station, and the second indication information may be anend marker packet.

For example, there is no data packet cached in the at least one PDCPentity, and all data packets cached in the first SDAP entity are datapackets to which no PDCP SN is allocated. In this case, the source basestation may send the end marker packet, so as to indicate the end ofdata packet sending.

For another example, none of the data packets cached in the at least onePDCP entity is allocated a PDCP SN, and all data packets cached in thefirst SDAP entity are data packets to which no PDCP SN is allocated. Inthis case, the source base station may send the end marker packet, so asto indicate the end of data packet sending.

Further, the first indication information includes a PDCP SN of the lastdata packet in the data packets cached in the at least one PDCP entity,or a next to-be-allocated PDCP SN.

For example, the at least one PDCP entity may allocate PDCP SNs to allthe data packets cached in the at least one PDCP entity. In this case,the source base station may send the end marker packet to a terminal, toindicate the end of sending the data packets cached in the first SDAPentity, and send the PDCP SN of the last data packet or the nextto-be-allocated PDCP SN, to indicate the end of sending the data packetscached in the at least one PDCP entity.

S1104. The second SDAP entity sends, to a terminal, a data packet thatis received by using the data tunnel #3.

Specifically, the second SDAP sends, based on a correspondence (or amapping relationship) between a QoS flow and a PDCP, the data packetreceived by the second SDAP entity to a corresponding PDCP entity, sothat the PDCP entity may perform further processing on the data packetwith reference to the prior art until the data packet is sent to theterminal by using a physical layer.

S1105. After determining, based on second indication information, thatall data packets received by using the data tunnel #3 have been sent,the second SDAP entity sends a data packet received from a core networkuser plane device.

Further, if a mapping relationship between a QoS flow and a DRB in thetarget base station is inconsistent with that in the source basestation, to ensure in-order data transmission of the QoS flow, forexample, a SDAP entity may deliver a data packet without carrying a PDCPSN to a PDCP entity after PDCP entities of all DRBs corresponding to thePDU session send PDCP SDUs with PDCP SNs.

Further, in another feasible manner, after having sent all PDCP SDUsthat carry PDCP SNs and that include a QoS flow, the PDCP entity of thetarget base station notifies the SDAP entity that all data packets ofthe QoS flow have been sent; then the SDAP starts to deliver, based on amapping relationship between a QoS flow and a DRB in the target basestation, a data packet that does not carry a PDCP SN and that is of theQoS flow to a PDCP entity corresponding to the DRB.

FIG. 12 is a schematic flowchart of a transmission method according tothis application. The method shown in FIG. 12 may be applied to aterminal handover process in a dual connectivity (DC) scenario, andspecifically, may be applied to an uplink transmission scenario in whichat least one QoS flow (denoted as a QoS flow #1) in a first PDU sessionis transferred from a source base station to a target base station. Thesource base station may be a master base station, or may be a secondarybase station. Correspondingly, the target base station may be asecondary base station, or may be a master base station. This is notlimited in this embodiment of this application.

S1210. When a source base station determines that a terminal no longersends a data packet of at least one quality of service (QoS) flow in afirst protocol data unit (PDU) session to the source base station, thesource base station generates start-to-send information.

S1220. The source base station sends the start-to-send information to atarget base station. The start-to-send information is used to instructthe target base station to send, to a core network user plane device, adata packet that is of the at least one QoS flow and that is sent by theterminal to the target base station. The start-to-send informationincludes an identity of the at least one QoS flow and an identity of thefirst PDU session; or the start-to-send information includes an identityof the at least one QoS flow and an identity of a first DRB, and thefirst DRB corresponds to the at least one QoS flow.

S1230. The target base station sends, to the core network user planedevice based on the start-to-send information, the data packet that isof the at least one QoS flow and that is sent by the terminal to thetarget base station.

Optionally, the start-to-send information is an end marker packet, orthe start-to-send information is a control plane message.

The transmission method shown in FIG. 12 is described in detail withreference to a transmission method shown in FIG. 13.

FIG. 13 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 13 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 13 may also be performed. In addition, steps in FIG.13 may be performed in an order different from that shown in FIG. 13,and not all the operations in FIG. 13 may be performed.

The method shown in FIG. 13 may be applied to a terminal handoverprocess in a dual connectivity (DC) scenario, and specifically, may beapplied to an uplink transmission scenario in which at least one QoSflow (denoted as a QoS flow #1) in a first PDU session is transferredfrom a source base station to a target base station. The source basestation may be a master base station, or may be a secondary basestation. Correspondingly, the target base station may be a secondarybase station, or may be a master base station. This is not limited inthis embodiment of this application.

In this embodiment of this application, before the QoS flow #1 istransferred to the target base station, a terminal sends a data packetof the QoS flow #1 to the source base station over a DRB (denoted as aDRB #1) between the terminal and the source base station, and the DRB #1corresponds to the QoS flow #1. If the source base station wants totransfer the QoS flow #1 to the target base station, the source basestation and the target base station may interact according to stepsS1301 and S1302.

S1301. The source base station sends a first request message to thetarget base station, where the first request message is used to requestto transfer the QoS flow #1 to the target base station.

Specifically, when determining to transfer the QoS flow #1 to the targetbase station, the source base station sends the first request message tothe target base station, and requests the target base station to acceptthe QoS flow #1 by using the first request message.

Optionally, the first request message may be an Xn interface message, orcarried in an Xn interface message.

S1302. If the target base station can accept the QoS flow #1, the targetbase station sends a first response message to the source base station.

For example, if the target base station determines that a resource of acell can provide a resource meeting the QoS flow #1, the target basestation sends the first response message to the source base station.

Then, data packet transmission may be performed according to thetransmission method in this embodiment of this application. Details aredescribed below in detail with reference to FIG. 13.

S1303. The source base station sends a first notification message to theterminal, where the first notification message is used to notify theterminal to send the data packet of the QoS flow #1 to the target basestation.

Specifically, the first notification message may be used to notify theterminal to map the QoS flow #1 to a DRB #2, and send the data packet ofthe QoS flow #1 to the target base station over the DRB #2.

It should be noted that alternatively, step S1303 may not be performed,but the target base station notifies the terminal to send the datapacket of the QoS flow #1 to the target base station. For example, thetarget base station sends the first notification message to theterminal, to notify the terminal to map the QoS flow #1 to the DRB #2,and send the data packet of the QoS flow #1 to the target base stationover the DRB #2.

S1304. The terminal sends the data packet of the QoS flow #1 to thetarget base station.

Specifically, after receiving the first notification message, theterminal stops sending the data packet of the QoS flow #1 to the sourcebase station, and starts to send the data packet of the QoS flow #1 overthe DRB #2 to the target base station.

For ease of understanding and description, data packets that are of theQoS flow #1 and that are sent by the terminal to the source base stationare denoted below as a data packet #1 to a data packet #i. Namely, thedata packets that are of the QoS flow #1 and that are sent by theterminal to the source base station are sequentially: the data packet#1, the data packet #2, . . . , and the data packet #i, where i is aninteger greater than or equal to 1.

After the terminal receives the first notification message, the terminalstarts to send a data packet after the data packet #i to the target basestation. Namely, the terminal successively sends a data packet #(i+1), adata packet #(i+2), . . . , and a data packet #N to the target basestation. In this embodiment of this application, it is assumed that atotal quantity of the data packets of the QoS flow #1 is N, where N isan integer greater than or equal to 2, and the data packet #N is thelast data packet in the data packets that are of the QoS flow #1 andthat are sent by the terminal to the target base station.

S1305. The terminal sends end packet information to the source basestation.

The end packet information is used to indicate information about thelast data packet, that is, information about the data packet #i, in thedata packets that are of the QoS flow #1 and that are sent by theterminal to the source base station.

Optionally, the end packet information may be an end marker packet. Theend marker packet includes an end marker and identity information of theQoS flow #1.

Optionally, the end packet information may also be a PDCP sequencenumber (SN) corresponding to the data packet #i.

It should be understood that an order of performing steps S1304 andS1305 is not limited in this embodiment of this application, that is,S1304 may be performed before S1305, or may be performed after S1305, oris performed simultaneously with S1305.

S1306. The source base station sends, to a core network user planedevice, data packets, that is, a data packet #1 to a data packet #i,that are of the QoS flow #1 and that are sent by the terminal to thesource base station.

S1307. The source base station sends start-to-send information to thetarget base station after determining, based on the end packetinformation, that all the data packet #1 to the data packet #i have beensent.

The start-to-send information includes an identity (ID) of the QoS flow#1 and an ID of a first PDU session, or the start-to-send informationincludes an identity of the QoS flow #1 and an ID of a DRB #2 (that is,a first DRB).

The start-to-send information is used to instruct the target basestation to start to send, to the core network user plane device, thedata packet that is of the QoS flow #1 and that is sent by the terminalto the target base station.

Further, the source base station may determine, based on an algorithm,time for sending the start-to-send information to the target basestation, for example, estimates, based on a data transmission latency,that the data packet sent by the target base station reaches the corenetwork user plane device before the data packet #i.

S1308. The target base station sends, to the core network user planedevice based on the start-to-send information, the data packets that areof the QoS flow #1 and that are sent by the terminal to the target basestation.

Specifically, after the source base station sends the data packet #i, ifit is found based on the end packet that there is no data packet of theQoS flow #1 after the data packet #i, that is, the terminal no longersends the data packet of the QoS flow #1 to the source base station, thesource base station sends the start-to-send information to the targetbase station. For example, if the data packet #i is followed by the endmarker packet, or a PDCP SN of the data packet #i is equal to a PDCP SNsent by the terminal to the source base station, the source base stationmay determine that there is no data packet of the QoS flow #1 after thedata packet #i. In this case, the source base station sends thestart-to-send information to the target base station. After receivingthe start-to-send information, the target base station starts to send,to the core network user plane device, the data packet #(i+1) to thedata packet #N that are received by the terminal over the DRB #1.

Optionally, the start-to-send information may be an Xn interfacemessage, or is carried in an Xn interface message.

Further, the start-to-send information may be end packet information,for example, the end marker packet, or the PDCP SN corresponding to thedata packet #i.

The source base station may send the end marker packet by using a dataforwarding tunnel between the source base station and the target basestation. The source base station may send the end marker packet receivedfrom the terminal to the target base station. Alternatively, the sourcebase station may generate the end marker packet by itself. For example,if the source base station determines that the terminal no longer sendsthe data packet of the QoS flow #1 to the source base station, thesource base station may generate the end marker packet.

Further, the start-to-send information may further carry indicationinformation (denoted as indication information #1) indicating atransmission direction of the data packet of the QoS flow #1. Theindication information #1 is used to indicate that the transmissiondirection of the data packet of the QoS flow #1 is an uplink.

According to the transmission method in this embodiment of thisapplication, after the source base station determines, based on the endpacket information, that all the data packets of the QoS flow to betransferred to the target base station have been sent by the terminal tothe source base station, and the source base station has sent all thedata packets that are of the QoS flow and that are received from theterminal to the core network user plane device, the source base stationuses the start-to-send information to instruct the target base stationto send the data packets of the QoS flow that is transferred from thesource base station to the target base station to the core network userplane device. Then, the target base station starts to send the datapackets of the QoS flow to the core network user plane device based onthe start-to-send information, so as to avoid out-of-order of the datapackets of the QoS flow.

FIG. 14 is a schematic flowchart of a transmission method according toanother embodiment of this application.

S1410. When a source base station determines that a terminal receives adata packet that is of at least one quality of service QoS flow in afirst PDU session and that is sent by the source base station, thesource base station generates start-to-send information.

S1420. The source base station sends the start-to-send information to atarget base station, where the start-to-send information is used toinstruct the target base station to start to send, to the terminal, adata packet that is of the at least one QoS flow and that is received bythe target base station from a core network user plane device Thestart-to-send information includes an identity of the at least one QoSflow and an identity of the first PDU session; or the start-to-sendinformation includes an identity of the at least one QoS flow and anidentity of a first data radio bearer DRB, and the first DRB correspondsto the at least one QoS flow.

S1430. The target base station sends the data packet that is of the atleast one QoS flow and that is received from the core network user planedevice to the terminal based on the start-to-send information.

Optionally, the start-to-send information is an end marker packet, orthe start-to-send information is a control plane message.

FIG. 15 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 15 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 15 may also be performed. In addition, steps in FIG.15 may be performed in an order different from that shown in FIG. 15,and not all the operations in FIG. 15 may be performed.

The method shown in FIG. 15 may be applied to a terminal handoverprocess in a dual connectivity (DC) scenario, and specifically, may beapplied to a downlink transmission scenario in which at least one QoSflow (denoted as a QoS flow #1) in a first PDU session is transferredfrom a source base station to a target base station. The source basestation may be a master base station, or may be a secondary basestation. Correspondingly, the target base station may be a secondarybase station, or may be a master base station. This is not limited inthis embodiment of this application.

In this embodiment of this application, before the QoS flow #1 istransferred to the target base station, a terminal sends a data packetof the QoS flow #1 to the source base station over a DRB (denoted as aDRB #1) between the terminal and the source base station, and the DRB #1corresponds to the QoS flow #1. If the source base station wants totransfer the QoS flow #1 to the target base station, the source basestation and the target base station may interact according to stepsS1501 and S1502.

S1501. The source base station sends a first request message to thetarget base station, where the first request message is used to requestto transfer the QoS flow #1 to the target base station.

Specifically, when determining to transfer the QoS flow #1 to the targetbase station, the source base station sends the first request message tothe target base station, and requests the target base station to acceptthe QoS flow #1 by using the first request message.

S1502. If the target base station can accept the QoS flow #1, the targetbase station sends a first response message to the source base station.

Then, data packet transmission may be performed according to thetransmission method in this embodiment of this application. Details aredescribed below in detail with reference to FIG. 15. The target basestation or the source base station sends a route changing message to anetwork element of a core network, to instruct the core network tochange a target routing address of the QoS flow #1.

S1503. The source base station sends end indication information to aterminal.

Specifically, when the source base station determines that the targetbase station can accept the QoS flow #1, for example, determines, basedon the first response message in step S1502, that the target basestation can accept the QoS flow #1, the source base station stopssending the data packet of the QoS flow #1 to the terminal, sends theend indication information to the terminal, and uses the end indicationinformation to instruct the source base station to end transmission ofthe data packets of the QoS flow #1.

Optionally, the end indication information may be an end marker packet.The end marker packet carries an ID of the QoS flow #1.

The end marker packet may be an empty data packet. In addition, anencapsulation header of the empty data packet may carry an end marker.For example, the end marker may be carried in a SDAP or PDCP extensionheader.

Optionally, the end indication information may be a PDCP SNcorresponding to a data packet #i. If the terminal has successfullyreceived a data packet prior to the PDCP SN, it may be determined thatall data packets that are of the QoS flow #1 and that are sent by thesource base station have been received.

Further, a UPF adds an end marker of a data packet of the QoS flow to adata packet sent to an MN, to indicate the end of sending data packetsthat are of the QoS flow and that are sent by the UPF to the MN. The UPFmay set the end marker of the QoS flow based on QoS flow transferindication information that is sent by the MN to the core network.Further, the UPF may further set the end marker of the QoS flow based ona path switch indication that is sent by the SN to the core network. Thepath switch indication is used to indicate that the UPF may start tosend the data packet of the QoS flow to the SN. In this way, the MNdetermines the end of sending the data packets that are of the QoS flow#1 and that are received from the UPF.

For ease of understanding and description, the data packets that are ofthe QoS flow #1 and that are sent by the source base station to theterminal over the DRB #1 are denoted below as a data packet #1 to a datapacket #i. That is, data packets that are of the QoS flow #1 and thatare sent by the source base station to the terminal are sequentially:the data packet #1, the data packet #2, . . . , and the data packet #i,where i is an integer greater than or equal to 1. After the source basestation sends the data packet #i, the source base station sends the endindication information to the terminal. It should be understood that theDRB #1 corresponds to the QoS flow #1, or a mapping relationship existsbetween the DRB #1 and the QoS flow #1.

S1504. The source base station receives feedback information sent by theterminal.

If the terminal has successfully received the data packet #1 to the datapacket #i, and determines, based on the end indication information sentby the source base station, that all the data packets that are of theQoS flow #1 and that are sent by the source base station have beensuccessfully received, the terminal sends the feedback information tothe source base station.

S1505. The source base station sends start-to-send information to thetarget base station based on the feedback information.

The start-to-send information is used to instruct the target basestation to send, to the terminal, the data packet that is of the QoSflow #1 and that is sent by a core network user plane device to thetarget base station. The start-to-send information includes an identityof the QoS flow #1 and an ID of a first PDU session, or thestart-to-send information includes an identity of the QoS flow #1 and anID of a first DRB (denoted as a DRB #2), and the DRB #2 corresponds tothe QoS flow #1.

For ease of understanding and description, data packets that are of theQoS flow #1 and that are sent by the core network user plane device tothe target base station are denoted below as a data packet #(i+1) to adata packet #N, where N is an integer greater than or equal to 2. Thatis, the data packets that are of the QoS flow #1 and that are sent bythe core network user plane device to the target base station aresequentially: the data packet #(i+1), the data packet #(i+2), . . . ,and the data packet #N.

S1506. The target base station sends a data packet #(i+1) to a datapacket #N to the terminal based on the start-to-send information.

Specifically, after the source base station receives the feedbackinformation sent by the terminal, the source base station sends thestart-to-send information to the target base station. After the targetbase station receives the start-to-send information, it may bedetermined that the source base station has sent all the data packetsthat are of the QoS flow #1 and that are received from the core networkuser plane device, and that the terminal has also successfully receivedthese data packets. Then the target base station starts to send the datapacket #(i+1) to the data packet #N to the terminal over the DRB #1.

Optionally, the start-to-send information may be the end indicationinformation, for example, an end marker packet, or a PDCP SNcorresponding to the data packet #i.

The source base station may send the end marker packet by using a dataforwarding tunnel between the source base station and the target basestation. The end marker packet may be an empty data packet. In addition,an encapsulation header of the empty data packet carries an end marker.For example, the end marker is carried in a GTPU extension header.

According to the transmission method in this embodiment of thisapplication, after the source base station determines, based on thefeedback information, that the terminal has successfully received thedata packets that are of the QoS flow and that are sent by the sourcebase station, the source base station uses the start-to-send informationto instruct the target base station to start to send the data packetsthat are of the QoS flow and that are received from the core networkuser plane device to the terminal, and the target base station starts tosend the data packets of the QoS flow to the terminal based on thestart-to-send information, so as to avoid out-of-order of the datapackets of the QoS flow.

FIG. 16 is a schematic flowchart of a transmission method according tothis application. It should be understood that FIG. 16 is a schematicflowchart of a transmission method according to an embodiment of thisapplication, and shows detailed communication steps or operations of themethod, but these steps or operations are merely examples. In thisembodiment of this application, other operations or variants of theoperations in FIG. 16 may also be performed. In addition, steps in FIG.16 may be performed in an order different from that shown in FIG. 16,and not all the operations in FIG. 16 may be performed.

The method shown in FIG. 16 may be applied to a terminal handoverprocess in a dual connectivity (DC) scenario, and specifically, may beapplied to a downlink transmission scenario in which at least one QoSflow (denoted as a QoS flow #1) in a first PDU session is transferredfrom a source base station to a target base station. The source basestation may be a master base station, or may be a secondary basestation. Correspondingly, the target base station may be a secondarybase station, or may be a master base station. This is not limited inthis embodiment of this application.

In this embodiment of this application, before the QoS flow #1 istransferred to the target base station, a terminal sends a data packetof the QoS flow #1 to the source base station over a DRB (denoted as aDRB #1) between the terminal and the source base station, and the DRB #1corresponds to the QoS flow #1. If the source base station wants totransfer the QoS flow #1 to the target base station, the source basestation and the target base station may interact according to stepsS1601 and S1602.

S1601. The source base station sends a first request message to thetarget base station, where the first request message is used to requestto transfer the QoS flow #1 to the target base station.

Specifically, when determining to transfer the QoS flow #1 to the targetbase station, the source base station sends the first request message tothe target base station, and requests the target base station to acceptthe QoS flow #1 by using the first request message.

Optionally, first indication information may be sent by using an Xninterface message.

S1602. If the target base station can accept the QoS flow #1, the targetbase station sends a first response message to the source base station.

Then, data packet transmission may be performed according to thetransmission method in this embodiment of this application. Details aredescribed below in detail with reference to FIG. 16.

S1603. The source base station sends end indication information to aterminal.

Specifically, when the source base station determines that the targetbase station can accept the QoS flow #1, for example, determines, basedon the first response message in step S1602, that the target basestation can accept the QoS flow #1, the source base station stopssending the data packet of the QoS flow #1 to the source base station,sends the end indication information to the terminal, and uses the endindication information to instruct the source base station to endtransmission of the data packets of the QoS flow #1.

Optionally, the end indication information may be an end marker packet.The end marker packet carries an ID of the QoS flow #1.

The end marker packet may be an empty data packet. In addition, anencapsulation header of the empty data packet may carry an end marker.For example, the end marker may be carried in a SDAP or PDCP header.

Optionally, the end indication information may be a PDCP SNcorresponding to a data packet #i. If the terminal has successfullyreceived a data packet prior to the PDCP SN, it may be determined thatall data packets that are of the QoS flow #1 and that are sent by thesource base station have been received.

For ease of understanding and description, the data packets that are ofthe QoS flow #1 and that are sent by the source base station to theterminal over the DRB #1 are denoted below as a data packet #1 to thedata packet #i. That is, the data packets that are of the QoS flow #1and that are sent by the source base station to the terminal aresequentially: the data packet #1, the data packet #2, . . . , and thedata packet #i, where i is an integer greater than or equal to 1. Afterthe source base station sends the data packet #i, the source basestation sends the end indication information to the terminal. It shouldbe understood that the DRB #1 corresponds to the QoS flow #1, or amapping relationship exists between the DRB #1 and the QoS flow #1.

S1604. The source base station receives feedback information sent by theterminal.

If the terminal has successfully received the data packet #1 to the datapacket #i, and determines, based on the end indication information sentby the source base station, that all the data packets that are of theQoS flow #1 and that are sent by the source base station have beensuccessfully received, the terminal sends the feedback information tothe source base station.

S1605. The target base station sends data packets, a data packet #(i+1)to a data packet #N, that are of the QoS flow #1 and that are receivedfrom a core network user plane device to the terminal.

For ease of understanding and description, the data packets that are ofthe QoS flow #1 and that are sent by the core network user plane deviceto the target base station are denoted below as the data packet #(i+1)to the data packet #N, where N is an integer greater than or equal to 2.That is, the data packets that are of the QoS flow #1 and that are sentby the core network user plane device to the target base station aresequentially: the data packet #(i+1), the data packet #(i+2), . . . ,and the data packet #N.

It should be understood that an order of performing steps S1605 andS1604 is not limited in this application, steps S1605 and S1604 may beperformed simultaneously, or one step may be performed before the other.

S1606. After receiving the data packets that are of the QoS flow #1 andthat are sent by the source base station and the target base station,the terminal first delivers, to an upper protocol layer, the datapackets that are of the QoS flow #1 and that are received from thesource base station, and then delivers the data packets that are of theQoS flow #1 and that are received from the target base station. That is,the terminal first delivers the data packet #1 to the data packet #N tothe upper protocol layer, and then delivers the data packet #(i+1) tothe data packet #N. Herein, the terminal may determine, based on the endindication information sent by the source base station, for example, byusing the end marker packet, the end of sending the data packets thatare of the QoS flow #1 and that are received from the source basestation.

According to the transmission method in this embodiment of thisapplication, the terminal may deliver, based on the end markerinformation sent by the source base station, the data packets that areof the QoS flow and that are received from the source base station tothe upper protocol layer, and then delivers the data packets that are ofthe QoS flow and that are received from the target base station.Therefore, in a process in which the QoS flow is transferred from thesource base station to the target base station, in-order transmission ofthe data packets of the QoS flow can be implemented, thereby ensuringquality of a service and avoid service quality degradation caused byout-of-order of the data packets.

According to the foregoing methods, FIG. 17 is a schematic diagram of adata transmission apparatus 10 according to an embodiment of thisapplication. As shown in FIG. 17, the apparatus 10 may be a terminaldevice, or may be a chip or a circuit, for example, may be a chip or acircuit disposed in a terminal. The terminal device may correspond tothe terminal device in the foregoing methods.

The apparatus 10 may include a processor 11 (that is, an example of aprocessing unit) and a memory 12. The memory 12 is configured to storean instruction, and the processor 11 is configured to execute theinstruction stored in the memory 12, so that the apparatus 10 performsthe steps performed by the terminal device in the foregoing methods.

Further, the apparatus 10 may further include an input interface 13(that is, an example of a communications unit) and an output interface14 (that is, another example of the communications unit). Further, theprocessor 11, the memory 12, the input interface 13, and the outputinterface 14 may communicate with each other by using an internalconnection path, to transmit a control signal and/or a data signal. Thememory 12 is configured to store a computer program, and the processor11 may be configured to invoke the computer program from the memory 12and run the computer program, to control the input interface 13 toreceive a signal and control the output interface 14 to send a signal,so as to complete the steps of the terminal device in the foregoingmethods. The memory 12 may be integrated in the processor 11, or may beseparate from the processor 11.

Optionally, if the apparatus 10 is the terminal device, the inputinterface 13 is a receiver, and the output interface 14 is atransmitter. The receiver and the transmitter may be a same physicalentity or different physical entities. When being the same physicalentity, the receiver and the transmitter may be collectively referred toas a transceiver.

Optionally, if the apparatus 10 is the chip or the circuit, the inputinterface 13 is an input interface, and the output interface 14 is anoutput interface.

In an implementation, functions of the input interface 13 and the outputinterface 14 may be implemented by using a transceiver circuit or adedicated transceiver chip. The processor 11 may be implemented by usinga dedicated processing chip, a processing circuit, a processor, or ageneral-purpose chip.

In another implementation, the terminal device provided in thisembodiment of this application may be implemented by using ageneral-purpose computer. To be specific, program code for implementingfunctions of the processor 11, the input interface 13, and the outputinterface 14 is stored in the memory 12, and the general-purposeprocessor implements the functions of the processor 11, the inputinterface 13, and the output interface 14 by executing the code in thememory 12.

Functions or actions of foregoing listed modules or units in thecommunications apparatus 10 are merely examples, and the modules orunits in the communications apparatus 10 may be configured to performthe actions or processing processes performed by the terminal device inany one of the foregoing methods. To avoid repetition, details areomitted herein.

For a concept, explanation, details, and other steps related to thetechnical solution of the apparatus 10 provided in this embodiment ofthis application, refer to the foregoing method or description about thecontent in another embodiment. Details are not described herein again.

FIG. 18 is a schematic structural diagram of a terminal device 20according to this application. The terminal device 20 may be configuredto perform actions of the terminal device described in any one of theforegoing methods. For ease of description, FIG. 18 shows maincomponents of the terminal device. As shown in FIG. 18, the terminaldevice 20 includes a processor, a memory, a control circuit, an antenna,and an input/output apparatus.

The processor is mainly configured to process a communications protocoland communications data, and control the entire terminal device, executea software program, and process data of the software program, forexample, configured to allow the terminal device to perform the actionsdescribed in the foregoing indication method embodiment of thetransmission precoding matrix. The memory is mainly configured to storethe software program and data, for example, store a codebook describedin the foregoing embodiment. The control circuit is mainly configured toperform conversion between a baseband signal and a radio frequencysignal, and process the radio frequency signal. The control circuittogether with the antenna may also be referred to as a transceiver,which is mainly configured to send and receive a radio frequency signalin a form of an electromagnetic wave. The input/output apparatus, suchas a touchscreen, a display screen, or a keyboard, is mainly configuredto receive data input by a user and data output by the user.

After the terminal device is powered on, the processor may read thesoftware program in a storage unit, interpret and execute an instructionof the software program, and process the data of the software program.When the data needs to be sent wirelessly, the processor performsbaseband processing on the to-be-sent data, and outputs a basebandsignal to the radio frequency circuit. The radio frequency circuitperforms radio frequency processing on the baseband signal, and sends aradio frequency signal by using the antenna in a form of anelectromagnetic wave. When data is sent to the terminal device, theradio frequency circuit receives a radio frequency signal by using theantenna, converts the radio frequency signal into a baseband signal, andoutputs the baseband signal to the processor, and the processor convertsthe baseband signal into data and processes the data.

A person skilled in the art may understand, for ease of description,FIG. 18 merely shows one memory and one processor. In an actual terminaldevice, there may be a plurality of processors and memories. The memorymay also be referred to as a storage medium or a storage device. This isnot limited in this embodiment of this application.

In an optional implementation, the processor may include a basebandprocessor and a central processor. The baseband processor is mainlyconfigured to process the communications protocol and the communicationsdata, and the central processor is mainly configured to control theentire terminal device, execute the software program, and process thedata of the software program. The processor in FIG. 18 integratesfunctions of the baseband processor and the central processing unit. Aperson skilled in the art may understand that the baseband processor andthe central processing unit may alternatively be independent processorsand interconnected by using a bus or another technology. A personskilled in the art may understand that the terminal device may include aplurality of baseband processors to adapt to different networkstandards, or the terminal device may include a plurality of centralprocessors to enhance its processing capability, and components of theterminal device may be connected by using various buses. The basebandprocessor may also be expressed as a baseband processing circuit or abaseband processing chip. The central processor may also be expressed asa central processing circuit or a central processing chip. The functionsof processing the communications protocol and the communication data maybe embedded in the processor, or may be stored in the storage unit in aform of a software program, and the processor executes the softwareprogram to implement the baseband processing function.

For example, in this embodiment of this application, an antenna and acontrol circuit that have a sending and receiving function may beconsidered as a transceiver unit 201 of the terminal device 20, and aprocessor having a processing function is considered as a processingunit 202 of the terminal device 20. As shown in FIG. 4, the terminaldevice 20 includes the transceiver unit 201 and the processing unit 202.The transceiver unit may also be referred to as a transceiver, atransceiver device, a transceiver apparatus, or the like. Optionally, adevice for implementing a receiving function in the transceiver unit 201may be considered as a receiving unit, and a device for implementing asending function in the transceiver unit 201 is considered as a sendingunit, that is, the transceiver unit 201 includes a receiving unit and asending unit. For example, the receiving unit may also be referred to asa receiver, a receiver device, or a receiver circuit, and the sendingunit may be referred to as a transmitter, a transmitter device, or atransmitter circuit.

According to the foregoing methods, FIG. 19 is a schematic diagram 2 ofa data transmission apparatus 30 according to an embodiment of thisapplication. As shown in FIG. 19, the apparatus 30 may be a networkdevice, or may be a chip or a circuit, for example, may be a chip or acircuit disposed in the network device. The network device correspondsto a network device in any one of the foregoing methods.

The apparatus 30 may include a processor 31 (that is, an example of aprocessing unit) and a memory 32. The memory 32 is configured to storean instruction, and the processor 31 is configured to execute theinstruction stored in the memory 32, so that the apparatus 30 performsthe steps performed by the network device in any one of the foregoingmethods.

Further, the apparatus 30 may further include an input interface 33(that is, an example of a communications unit) and an output interface34 (that is, another example of the processing unit). Still further, theprocessor 31, the memory 32, the input interface 33, and the outputinterface 34 may communicate with each other by using an internalconnection path, to transmit a control signal and/or a data signal. Thememory 32 is configured to store a computer program, and the processor31 may be configured to invoke the computer program from the memory 32and run the computer program, to control the input interface 33 toreceive a signal and control the output interface 34 to send a signal,so as to complete the steps of the network device in the foregoingmethods 200. The memory 32 may be integrated in the processor 31, or maybe separate from the processor 31, to control the input interface 33 toreceive the signal, and control the output interface 34 to send thesignal, so as to complete the steps of the network device in theforegoing methods. The memory 32 may be integrated in the processor 31,or may be separate from the processor 31.

Optionally, if the apparatus 30 is the network device, the inputinterface 33 is a receiver, and the output interface 34 is atransmitter. The receiver and the transmitter may be a same physicalentity or different physical entities. When being the same physicalentity, the receiver and the transmitter may be collectively referred toas a transceiver.

Optionally, if the apparatus 30 is the chip or the circuit, the inputinterface 33 is an input interface, and the output interface 34 is anoutput interface.

Optionally, if the apparatus 30 is a chip or a circuit, the apparatus 30may either not include the memory 32, and the processor 31 may read aninstruction (a program or code) in an external memory of the chip toimplement the functions of the network device in any one of theforegoing methods.

In an implementation, functions of the input interface 33 and the outputinterface 34 may be implemented by using a transceiver circuit or adedicated transceiver chip. The processor 31 may be implemented by usinga dedicated processing chip, a processing circuit, a processor, or ageneral-purpose chip.

In another implementation, the network device provided in thisembodiment of this application may be implemented by using ageneral-purpose computer. To be specific, program code for implementingfunctions of the processor 31, the input interface 33, and the outputinterface 34 is stored in the memory, and the general-purpose processorimplements the functions of the processor 31, the input interface 33,and the output interface 34 by executing the code in the memory.

Modules or units in the communications apparatus 30 may be configured toperform various actions or processing processes performed by the networkdevice in any one of the foregoing methods. To avoid repetition, detailsare omitted herein.

For a concept, explanation, details, and other steps related to thetechnical solution of the apparatus 30 provided in this embodiment ofthis application, refer to the foregoing method or description about thecontent in another embodiment. Details are not described herein again.

FIG. 20 is a schematic structural diagram of a network device accordingto an embodiment of this application. The network device may beconfigured to implement functions of the network device in any one ofthe foregoing methods. For example, FIG. 20 may be a schematicstructural diagram of a base station. As shown in FIG. 20, the basestation may be applied to the system shown in FIG. 1. The base station40 includes one or more radio frequency units, for example, a remoteradio unit (RRU) 401 and one or more baseband units (BBUs) (which mayalso be referred to as digital units, digital unit (DU)) 402. The RRU401 may be referred to as a transceiver unit, a transceiver, atransceiver circuit, a transceiver device, or the like, and may includeat least one antenna 4011 and a radio frequency unit 4012. The RRU 401is mainly configured to send and receive a radio frequency signal, andperform conversion between the radio frequency signal and the basebandsignal, for example, configured to send a signaling message described inthe foregoing embodiment to the terminal device. The BBU 402 is mainlyconfigured to perform baseband processing, control the base station, andthe like. The RRU 401 and the BBU 402 may be physically disposedtogether, or may be physically separated, that is, a distributed basestation.

The BBU 402 is a control center of the base station, may also bereferred to as a processing unit, and is mainly configured to performbaseband processing functions such as channel coding, multiplexing,modulation, and spread spectrum. For example, the BBU (processing unit)402 may be used to control the base station 40 to perform the operationprocedures of the network device in the foregoing method embodiments.

In an example, the BBU 402 may include one or more boards, and aplurality of boards may jointly support a radio access network (such asan LTE system or a 5G system) of a single radio access technology, ormay support radio access networks of different radio accesstechnologies. The BBU 402 further includes a memory 4021 and a processor4022. The memory 4021 is configured to store a necessary instruction anddata. For example, the memory 4021 stores a codebook in the foregoingembodiment. The processor 4022 is configured to control the base stationto perform a necessary operation, for example, configured to control thebase station to perform the operation procedures of the network devicein the foregoing method embodiments. The memory 4021 and the processor4022 may serve one or more boards. In other words, the memory and theprocessor may be separately configured on each board. Alternatively, asame memory and processor may be jointly configured on a plurality ofboards. In addition, a necessary circuit may be disposed on each board.

In a possible implementation, with the development of a System-On-a-Chip(SoC) technology, some or all of the functions of the 402 part and the401 part may be implemented by the SoC technology, for example,implemented by a base station function chip. The base station functionchip integrates devices such as a processor, a memory, and an antennainterface, a program of related functions of the base station is storedin the memory, and the processor executes the program to implement therelated functions of the base station. Optionally, the base stationfunction chip can also read the external memory of the chip, toimplement the related functions of the base station.

It should be understood that a structure of the base station shown inFIG. 20 is merely a possible form, and should not be construed as anylimitation on the embodiments of this application. This application doesnot preclude a possibility of other forms of base station structure thatmay occur in the future.

According to the methods provided in the embodiments of thisapplication, an embodiment of this application further provides acommunications system, and the communications system includes theforegoing network device and one or more terminal devices.

It should be understood that in the embodiment of this application, theprocessor may be a central processing unit (CPU), or the processor maybe another general-purpose processor, a digital signal processor (DSP),an application-specific integrated circuit (ASIC), a field programmablegate array (FPGA), or another programmable logic device, a discrete gateor transistor logic device, a discrete hardware component, or the like.The general-purpose processor may be a microprocessor, the processor maybe any conventional processor, or the like.

It may be further understood that the memory in the embodiments of thisapplication may be a volatile memory or a nonvolatile memory, or mayinclude a volatile memory and a nonvolatile memory. The nonvolatilememory may be a read-only memory (ROM), a programmable read-only memory(programmable ROM, PROM), an erasable programmable read-only memory(erasable PROM, EPROM), an electrically erasable programmable read-onlymemory (electrically EPROM, EEPROM), or a flash memory. The volatilememory may be a random access memory (RAM), used as an external cache.Through example but not restrictive description, many forms of randomaccess memories (RAM) may be used, for example, a static random accessmemory (SRAM), a dynamic random access memory (DRAM), a synchronousdynamic random access memory (synchronous DRAM, SDRAM), a double datarate synchronous dynamic random access memory (double data rate SDRAM,DDR SDRAM), an enhanced synchronous dynamic random access memory(enhanced SDRAM, ESDRAM), a synchronous link dynamic random accessmemory (synchlink DRAM, SLDRAM), and a direct rambus dynamic randomaccess memory (direct rambus RAM, DR RAM).

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the foregoing embodiments may beimplemented completely or partially in a form of a computer programproduct. The computer program product includes one or more computerinstructions or a computer program. When the computer programinstruction or the computer program is loaded and executed on acomputer, the procedure or functions according to the embodiments ofthis application are all or partially generated. The computer may be ageneral-purpose computer, a dedicated computer, a computer network, orother programmable apparatuses. The computer instructions may be storedin a computer-readable storage medium, or may be transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, infrared, radio, andmicrowave) manner. The computer-readable storage medium may be anyusable medium accessible to a computer, or a data storage device such asa server or a data center, integrating one or more usable media. Theusable medium may be a magnetic medium (for example, a soft disk, a harddisk, or a magnetic tape), an optical medium (for example, a DVD), or asemiconductor medium. The semiconductor medium may be a solid-statedrive.

It should be understood that the term “and/or” in this specificationdescribes only an association relationship for describing associatedobjects and represents that three relationships may exist. For example,A and/or B may represent the following three cases: Only A exists, bothA and B exist, and only B exists. In addition, the character “/” in thisspecification generally indicates an “or” relationship between theassociated objects.

It should be understood that sequence numbers of the foregoing processesdo not mean execution sequences in various embodiments of thisapplication. The execution sequences of the processes should bedetermined according to functions and internal logic of the processes,and should not be construed as any limitation on the implementationprocesses of the embodiments of this application.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this application. It may be clearly understoodby a person skilled in the art that, for the purpose of convenient andbrief description, for a detailed working process of the foregoingsystem, apparatus, and unit, reference may be made to a correspondingprocess in the foregoing method embodiments, and details are notdescribed herein again. In the several embodiments provided in thisapplication, it should be understood that the disclosed system,apparatus, and method may be implemented in other manners. For example,the described apparatus embodiment is merely an example. For example,the unit division is merely logical function division and may be anotherdivision in actual implementation. For example, a plurality of units orcomponents may be combined or integrated into another system, or somefeatures may be ignored or not performed. In addition, the displayed ordiscussed mutual couplings or direct couplings or communicationconnections may be implemented by using some interfaces. The indirectcouplings or communication connections between the apparatuses or unitsmay be implemented in electrical, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected based on actualrequirements to achieve the objectives of the solutions of theembodiments. In addition, functional units in the embodiments of thisapplication may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units are integratedinto one unit. When the functions are implemented in a form of asoftware functional unit and sold or used as an independent product, thefunctions may be stored in a computer-readable storage medium. Based onsuch an understanding, the technical solutions of this applicationessentially, or the part contributing to the prior art, or some of thetechnical solutions may be implemented in a form of a software product.The computer software product is stored in a storage medium, andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, or a network device) to performall or some of the steps of the methods described in the embodiments ofthis application. The foregoing storage medium includes: any medium thatcan store program code, such as a USB flash drive, a removable harddisk, a read-only memory (ROM), a random access memory (RAM), a magneticdisk, or an optical disc.

The foregoing descriptions are merely specific implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication shall fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

What is claimed is:
 1. A transmission method during a handover,comprising: sending, by a source access network device, data packets ofa quality of service (QoS) flow and a first end marker packet to a firstcore network user plane device over a first data tunnel, wherein thedata packets were previously received by the source access networkdevice from the first core network user plane device, the first endmarker packet includes an identifier of the QoS flow, the first endmarker packet indicates an end of sending data packets of the QoS flowto the first core network user plane device, and the first data tunnelis corresponding to a first protocol data unit (PDU) session; sending,by the first core network user plane device, the data packets receivedfrom the source access network device and a second end marker packet toa second core network user plane device over a second data tunnel,wherein the second end marker packet is corresponding to an evolvedpacket system (EPS) bearer, and the second data tunnel is correspondingto the EPS bearer; and sending, by the second core network user planedevice, the data packets received from the first core network user planedevice to a target access network device.
 2. The method of claim 1,further comprising: determining, by the first core network user planedevice, the second data tunnel based on a correspondence between the QoSflow and the EPS bearer.
 3. The method of claim 1, further comprising:sending, by the second core network user plane device, the second endmarker packet to the target access network device.
 4. The method ofclaim 1, wherein the first end marker packet is a non-data packet, andan end marker is included in a general packet radio service tunnelprotocol user plane (GTPU) header of the non-data packet.
 5. The methodof claim 1, wherein the first core network user plane device is a userplane function (UPF), and the second core network user plane device is aserving gateway (S-GW).
 6. The method of claim 1, further comprising:generating, by the first core network user plane device, a second endmarker packet based on the first end marker packet.
 7. A transmissionsystem, comprising: a source access network device, a first core networkuser plane device, a second core network user plane device, wherein: thesource access network device is configured to send data packets of aquality of service (QoS) flow and a first end marker packet to the firstcore network user plane device over a first data tunnel, wherein thedata packets were previously received by the source access networkdevice from the first core network user plane device, the first endmarker packet includes an identifier of the QoS flow, the first endmarker packet indicates an end of sending data packets of the QoS flowto the first core network user plane device, and the first data tunnelis corresponding to a first protocol data unit (PDU) session; the firstcore network user plane device is configured to send data packetsreceived from the source access network device and a second end markerpacket to the second core network user plane device over a second datatunnel, wherein the second end marker packet is corresponding to anevolved packet system (EPS) bearer, and the second data tunnel iscorresponding to the EPS bearer; and the second core network user planedevice is configured to send the data packets received from the firstcore network user plane device to a target access network device.
 8. Thetransmission system of claim 7, wherein the first core network userplane device is further configured to determine the second data tunnelbased on a correspondence between the QoS flow and the EPS bearer. 9.The transmission system of claim 7, wherein the second core network userplane device is further configured to send the second end marker packetto the target access network device.
 10. The transmission system ofclaim 7, wherein the first end marker packet is a non-data packet, andan end marker is included in a general packet radio service tunnelprotocol user plane (GTPU) header of the non-data packet.
 11. Thetransmission system of claim 7, wherein the first core network userplane device is a user plane function (UPF), and the second core networkuser plane device is a serving gateway (S-GW).
 12. The transmissionsystem of claim 7, wherein the first core network user plane device isfurther configured to generate a second end marker packet based on thefirst end marker packet.
 13. A transmission apparatus, comprising: areceiver configured to receive, from a source access network device,data packets of a quality of service (QoS) flow and a first end markerpacket over a first data tunnel, wherein the data packets are receivedby the source access network device from a first core network user planedevice, the first end marker packet indicates an end of sending datapackets of the QoS flow to the first core network user plane device, andthe first data tunnel is corresponding to a first protocol data unit(PDU) session; and a transmitter configured to send the received datapackets and a second end marker packet to a second core network userplane device over a second data tunnel, wherein the second end markerpacket is corresponding to an evolved packet system (EPS) bearer, andthe second data tunnel is corresponding to the EPS bearer.
 14. Thetransmission apparatus of claim 13, further comprising a processorconfigured to determine the second data tunnel based on a correspondencebetween a quality of service (QoS) flow and the EPS bearer.
 15. Thetransmission apparatus of claim 13, wherein the first end marker packetis a non-data packet, a general packet radio service tunnel protocoluser plane (GTPU) header of the non-data packet includes an end marker.16. The transmission apparatus of claim 13, wherein the first corenetwork user plane device is a user plane function (UPF), the secondcore network user plane device is a serving gateway (S-GW).
 17. Anon-transitory computer readable medium, comprising computer readableinstructions stored thereon which, when executed by a processor, cause acommunication device to implement: receiving, from a source accessnetwork device, data packets of a quality of service (QoS) flow and afirst end marker packet over a first data tunnel, wherein the datapackets are received by the source access network device from a firstcore network user plane device, the first end marker packet indicates anend of sending data packets of the QoS flow to the first core networkuser plane device, and the first data tunnel is corresponding to a firstprotocol data unit (PDU) session and transmitting the received datapackets and a second end marker packet to a second core network userplane device over a second data tunnel, wherein the second end markerpacket is corresponding to an evolved packet system (EPS) bearer, andthe second data tunnel is corresponding to the EPS bearer.
 18. Thenon-transitory computer readable medium of claim 17, wherein the firstend marker packet is a non-data packet, a general packet radio servicetunnel protocol user plane (GTPU) header of the non-data packet includesan end marker.